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Lemon Filling
1 cup sugar. 2½ tablespoons flour Grated rind 2 lemons 1/4 cup lemon juice 1 egg 1 teaspoon butter Mix sugar and flour, add grated rind, lemon juice, and egg slightly beaten. Put butter in saucepan; when melted, add mixture, and stir constantly until boiling-point is reached. Care must be taken that mixture does not adhere to bottom of saucepan. Cool before spreading.
A lemon curd thickened with flour rather than yolks alone, meant to go between cake layers. The printed ingredient line has been garbled in transmission, so read the method carefully before starting.
- The missing sugarThe instructions begin "Mix sugar and flour," but no sugar appears in the ingredient list. Comparable lemon fillings of this period use about 1 cup granulated sugar to this quantity of juice and rind; the omission is a printing fault, not a sugarless filling.
- "21½ tablespoons flour"Almost certainly a typesetting slip for 2½ tablespoons. Twenty-one tablespoons of flour to a quarter cup of juice would produce paste, not filling. Treat 2½ tablespoons (about 20 g) as the working figure.
- Rind before juiceGrate the zest off the lemons while they are still whole and firm. Two lemons yield roughly 2 tablespoons of zest and, conveniently, close to the ¼ cup of juice called for.
- The hinge: constant stirring, low heatEgg and flour together will scramble and catch if the pan runs hot. Use a heavy saucepan over medium-low heat, stir into the corners with a flat-edged spoon or spatula, and stop the moment the mixture bubbles once or twice. Flour needs that brief boil to lose its raw taste; the egg will not curdle if it is moving.
- Butter firstThe teaspoon of butter is melted in the pan before the rest goes in. Whatever the intent, a filmed pan can only help with the warning that follows, that the mixture must not adhere to the bottom.
- Cooling and consistencyIt thickens considerably as it cools. Press plastic wrap or buttered paper on the surface to stop a skin forming, and chill until it holds a shape before spreading.
- YieldAbout 1 cup, enough to fill one two-layer 8- or 9-inch cake. It keeps three or four days covered in the refrigerator.
Lemon filling of this type sits among the cake fillings in the Boston Cooking School tradition. Flour-thickened lemon curd was the economical version of the form: it stretched one egg and a couple of lemons across a whole cake, where English-style lemon curd uses several yolks and a good deal more butter. The garbled measurement here is a reminder that these books were reset repeatedly for new printings, and errors crept in between editions.